变质作用、板块构造及超级大陆旋回

麻粒岩相超高温变质作用（GUHTM）主要发育于新太古代至寒武纪岩石中；推测在深部较年轻的，特别是新生代造山带岩石中也会有GUHTM存在。岩石中最初出现GUHTM记录意味着产生瞬时极高热流处的地球动力学发生了改变。许多GUHTM带可能发育于类似现代大陆弧后的构造背景中。在较热的地球上，超大陆及其裂解形成的循环组合，尤其是经岩石圈减薄的洋盆卷入到其外翻过程中可能产生比现代太平洋边缘更热的大陆弧后。中温榴辉岩 高压麻粒岩相变质作用（EHPGM）也是最先发现于新太古代岩石记录中，并发育于从元古宙至古生代岩石中。EHPGM带是对GUHTM带的补充，并经常认为是记录了从俯冲至碰撞造山作用的过程。在元古宙岩石记录中的蓝片岩明显记录了与现代俯冲作用相关的低热流梯度。以发育柯石英(±硬柱石)或金刚石为特征的硬柱石蓝片岩和榴辉岩（高压变质作用，HPM）及超高压变质岩（UHPM）主要是在显生宙形成。HPMUHPM记录了显生宙俯冲碰撞造山带早期碰撞过程中的低热流梯度及陆壳的深俯冲作用。尽管与直觉不同，在超级大陆聚敛期（Wilson旋回洋盆打开和关闭）的大陆地块增生过程，许多HPMUHPM带看来确实是通过小洋盆关闭而发育起来的，反映双重热体制的双重变质带仅发育于新太古代以来的岩石记录中。双重热体制是现代板块构造的特点，而双重变质作用则是板块构造在岩石记录中的特征性标志。尽管构造样式很可能不同，新太古代以来GUHTM和EHPGM带的发育证明“元古宙板块构造体制”的开始。以冷俯冲和大陆地壳深俯冲至地幔，以及其中的部分又从深达300 km处发生折返为标志，“元古宙板块构造体制”在新元古代进化为“现代板块构造体制”，这个转变可由岩石中的HPMUHPM证明。记录这种极端条件的变质带年龄是不一致的，而变质作用发生时间与各大陆岩石圈聚合到超级克拉通（如Superia/Sclavia）或超级大陆（如Nuna (Columbia), Rodinia, Gondwana, 和Pangea）的时间却是一致的。

METAMORPHISM, PLATE TECTONICS, AND THE SUPERCONTINENT CYCLE

Granulite facies ultrahigh temperature metamorphism (G - UHTM) is documented in the rock record predominantly from Neoarchean to Cambrian; G - UHTM facies series rocks may be inferred at depth in younger, particularly Cenozoic orogenic systems. The first occurrence of G - UHTM in the rock record signifies a change in geodynamics that generated transient sites of very high heat flow. Many G - UHTM belts may have developed in settings analogous to modern continental backarcs. On a warmer Earth, the cyclic formation of supercontinents and their breakup, particularly by extroversion, which involved destruction of ocean basins floored by thinner lithosphere, may have generated hotter continental backarcs than those associated with the modern Pacific rim. Medium-temperature eclogite-high-pressure granulite metamorphism (E - HPGM) also is first recognized in the Neoarchean rock record and occurs at intervals throughout the Proterozoic and Paleozoic rock record. E - HPGM belts are complementary to G - UHTM belts and are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record; they record the low thermal gradients associated with modern subduction. Lawsonite blueschists and eclogites (high-pressure metamorphism, HPM) and ultrahigh pressure metamorphism (UHPM) characterized by coesite (±lawsonite) or diamond are predominantly Phanerozoic phenomena. HPM - UHPM registers the low thermal gradients and deep subduction of continental crust during the early stage of the collision process in Phanerozoic subduction-to-collision orogens. Although perhaps counterintuitive, many HPM - UHPM belts appear to have developed by closure of small ocean basins in the process of accretion of a continental terrane during a period of supercontinent introversion (Wilson cycle ocean basin opening and closing). A duality of metamorphic belts-reflecting a duality of thermal regimes-appears in the record only since the Neoarchean Era. A duality of thermal regimes is the hallmark of modern plate tectonics and the duality of metamorphic belts is the characteristic imprint of plate tectonics in the rock record. The occurrence of both G - UHTM and E - HPGM belts since the Neoarchean manifests the onset of a "Proterozoic plate tectonics regime", although the style of tectonics likely involved differences. The "Proterozoic plate tectonics regime" evolved during a Neoproterozoic transition to the "modern plate tectonics regime" characterized by colder subduction and subduction of continental crust deep into the mantle and its (partial) return from depths of up to 300 km, as chronicled by the appearance of HPM - UHPM in the rock record. The age distribution of metamorphic belts that record extreme conditions of metamorphism is not uniform, and metamorphism occurs in periods that correspond to amalgamation of continental lithosphere into supercratons (e.g. Superia/Sclavia) or supercontinents (e.g. Nuna (Columbia), Rodinia, Gondwana, and Pangea).